Magnetic brush development apparatus

ABSTRACT

XEROGRAPHIC APPARATUS FOR THE MAGNETIC BRUSH DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES WITH A TWO-COMPONENT MAGNETIC DEVELOPER. THE APPARATUS INCLUDES A PLURALITY OF ROLLERS WITH MAGNETIC FIELDS EXTENDING THEREFROM POSITIONED ADJACENT A LATENT ELECTROSTATIC IMAGE BEARING SURFACE TO BE DEVELOPED WITH THEIR AXES OF ROTATION PARALLEL TO EACH OTHER. DRIVE MEANS ARE PROVIDED TO ROTATE EACH ROLLER IN A DIRECTION OPPOSITE TO EACH ADJACENT ROLLER. IN THIS MANNER, ALTERNATE ROLLERS FUNCTION AS MAGNETIC BRUSH DEVELOPING ROLLERS WHILE THE INTERMEDIATE ROLLERS FUNCTION AS DEVELOPER TRANSPORT ROLLERS TO MAGNETICALLY TRANSPORT THE DEVELOPER FROM ONE DEVELOPING ROLLER TO THE NEXT. WHEN A SUMP OF DEVELOPER IS PROVIDED ADJACENT THE LOWERMOST ROLLER, GRAVITY MAY BE UTILIZED TO RETURN DEVELOPER FROM THE UPPERMOST ROLLER TO THE SUMP. BAFFLES MAY ALSO BE EMPLOYED TO CROSS-MIX DEVELOPER RETURNING TO THE SUMP.

March 1971 J. MAKSYMIAK 3,572,289

MAGNETIC BRUSH DEVELOPMENT APPARATUS Filed Sept. 23, 1968 2 SheetsSheet 1 INVENTOR. JOHN MAKSYM IAK ATTORNE Y March 1971 J. MAKSYMIAK 3,572,289

MAGNETIC BRUSH DEVELOPMENT APPARATUS Filed Sept. 23, 1968 2 Sheets-Sheet 2 United States Patent Ofice 3,572,289 MAGNETIC BRUSH DEVELOPMENT APPARATUS John Maksymiak, Penfield, N.Y., assignor to Xerox Corporation, Rochester, NY. Filed Sept. 23, 1968, Ser. No. 761,723 Int. Cl. 1305b 5/02 US. Cl. 118-637 5 Claims ABSTRACT OF THE DISCLOSURE as developer transport rollers to magnetically transport the developer from one developing roller to the next. When a sump of developer is provided adjacent the lowermost roller, gravity may be utilized to return developer from the uppermost roller to the sump. Bailies may also be employed to cross-mix developer returning to the sump.

This invention relates in general to xerographic development and in particular to apparatus for the magnetic brush development of latent electrostatic images.

In the practice of xerography,as described in US. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

(The latent electrostatic image can then be developed 'by contacting it with a finely divided electrostatically attractable material such as a resinous powder. The powder is held in image areas by the elecrtostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited; and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity withthe light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed to thereby form a permanent print.

The electrostatically attractable developing material commonly used in xerography consists of a pigmented resinous powder referred to here as toner and a carrier of larger granular beads formed of glass, sand or steel and having an exterior of a material removed in the triboelectric series from the toner so that a triboelectric charge is generated between the toner powder and the granular carrier. Such charge causes the toner to adhere to the carrier. The carrier also provides mechanical control so that the toner can be readily handled and brought into contact with the exposed xerographic surface. The toner is then attracted to the electrostatic image from the carrier to produce a visible powder image on the xerographic surface.

One common technique employed today for bringing 3,572,289 Patented Mar. 23, 1971 developer into contact with a latent electrostatic imagebearing surface for its development is the magnetic brush system. In the magnetic brush system, the carrier employed is magnetic in nature, that is, it responds when placed in a magnetic field to form a brush-like array with bristles corresponding to the magnetic field producing means. Thus, when a quantity of two-component developer mix having magnetic carrier granules is entrained by a magnet, movement of the magnet relative to the latent electrostatic image may move the entrained developer across the image to deposit the toner in a configuration corresponding to the image being developed. This occurs when the charge on image area portions of the photoconductor exceeds the attraction of the carrier surface for the oppositely charged toner.

Typical of magnetic brush development systems employed today is that disclosed in US. Pat. No. 3,003,462 to Streich. According to that disclosure, a cylinder formed with magnetic washers having alternate north and south poles, is positioned adjacent the surface being developed. The lower portion of the magnetic cylinder is submerged in a reservoir or sump of magnetic developer material while the upper portion of the magnetic cylinder is located adjacent the path of movement of a latent electrostatic image-bearing surface. When the magnetic roller is rotated and the image being developed is moved across the cylinder, magnetic bristles are formed on the surface of the roller which contact the image-bearing surface for its development. Other types of magnetic brush development systems are those disclosed in US. Pat. No. 2,975,758 to Bird and US. Pat. No. 2,874,063 to Greig.

In each of these systems a magnetic brush is formed due to the presence of the magnetic field producing means. Plural brushes can be used in a single development zone to increase development capabilities in either of two fashions. The first is by the costly procedure of providing a separate sump for each brush. The second is by limiting the location of the plurality of brushes to beneath the surface being developed so that the plural brushes all have their lower extents in a common sump. In addition, known magnetic brush development systems require supplemental driven mechanisms to achieve crossmixing of the developer so that an even concentration of developer extends across the sump and development zone.

The magnetic brush development apparatus of the instant invention is adapted to form a plurality of magnetic brushes in a single development zone over a wide latitude of arcs or areas adjacent a continuous photoconductive surface. This is achieved while yet using only a single developer sump. The system also has the capability of cross-mixing the developer without employing supplemental driven mechanisms. Furthermore, the apparatus has the capability of agitating the developer in the development zone to present additional freshly toned developer to the image-bearing surface being developed.

It is therefore an object of the present invention to develop latent electrostatic images with two-component magnetic developer.

It is a further object of the instant invention to develop latent electrostatic images with a plurality of magnetic brushes over a Wide latitude of areas of a continuou xerographic surface.

It is a further object of the instant invention to cause agitation and turbulence within image developing magnetic brushes for the presentation of fresh developer at various portions along the development zone.

It is a further object of the instant invention to employ a single developes sump to feed a plurality of magnetic brushes.

It is a further object to easily cross-mix developer in a multiple magnetic brush system.

It is a further object of the invention to employ magnetic rollers to alternately convey developer and to use it for development.

These and other objects of the instant invention are obtained by magnetic brush development apparatus which includes a plurality of rollers having magnetic lines of force extending therefrom. The rollers are positioned adjacent a latent electrostatic image bearing surface to be developed with their axes of rotation parallel to each other. The rollers are driven in directions opposite to each adjacent roller so that every other roller functions as a magnetic brush developing roller while each intermediate roller functions as a developer transport roller, magnetically transporting the developer from one developing roller to the next. A sump of developer is provided adjacent the lowermost roller to feed the system while gravity is utilized to return developer from the uppermost roller to the sump. Cross-mix bafiies are employed to cross-mix developer returning to the sump.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic sectional view illustrating a xerographic reproducing machine adapted for continuous and automatic use and which employs the magnetic brush development system of the instant invention;

FIG. 2 is an enlarged perspective showing of the magnetic brush development apparatus shown in FIG. 1 with parts broken away for clarity, and

FIG. 3 is an enlarged diagrammatic sectional view similar to that shown in FIG. 1 but illustrating an alternate arrangement of magnetic rollers.

Shown in FIG. 1 is a xerographic machine employing the magnetic brush development apparatus of the instant invention. The elements of this machine, which are constructed for continuous and automatic operation, are all conventional in the xerographic art except for the novel development apparatus, which forms the basis of the instant application. For the purpose of the present disclosure, the several xerographic processing station in the path of movement of the xerographic surface may be briefly described as follows:

A charging station A, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic surface;

An exposure station B, at which the light or radiation pattern of copy to be reproduced is projected onto the xerographic surface to dissipate the charge in the exposed areas thereof to thereby leave a latent electrostatic image of the copy to be reproduced;

A developing station C, at which a xerographic developing material, including toner particles having an electrostatic charge opposite to that of the electrostatic latent image, are moved into contact with the image bearing surface, whereby the toner particles adhere to the electrostatic latent image to form a xerograpln'c powdered image in the configuration of the copy being reproduced;

A transfer station D, at which the xerographic powder image is electrostatically transferred from the xerographic surface to a transfer material or a support surface, and

A cleaning and discharge station E, at which the xerographic surface is brushed to remove residual toner particles remaining thereon after image transfer, and at which the surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

The latent electrostatic images to be developed are formed on a xerographic surface formed in the shape of an endless belt. The surface 10 could be of any configuration including a disposable photoconductive web or sheets as well as a drum shaped reusable photoconductor. The belt is adapted to be rotated about three supporting rollers, 12, 14 and 16, two of which, 14 and 16 are idler 4 rollers and the third of which, 12, is a power imparting roller driven by any convenient power source 18. The movement of the xerographic belt permits its surface to be moved past the various xerographic processing stations including the development zone C.

The xerographic developing apparatus is provided within a developer housing 20 formed of a non-magnetic material such as of metal, plastic or the like. The lower portion of the housing is trough-like in configuration to define a sump 22 to support a quantity of two-component magnetic developer. The developer employed includes image developing toner particles and larger carrier granules having magnetic properties. The carrier granules may be metallic or other materials having magnetic properties either uncoated or coated with a carrier coating material so that a triboelectric charge is generated between it and the toner upon mutual interaction. This charge is necessary to effect the xerographic development of the images. Examples of such magnetic developer are described in US. Pat. No. 2,874,063 to Greig.

The housing is supported adjacent its sides by sup port members 24 which are part of the xerographic reproducing machines and are spaced a distance which is larger than the width of the belt shaped photoconductor.

Located within the housing 20 are a plurality of magnetic rollers or cylinders 25 and 26. Each of the magnetic rollers is formed of a plurality of disc shaped pole pieces 27 separated by disc shaped magnetic washers 28 having alternating north and south pole sections arranged so that lines of magnetic force may emanate therefrom for use in entraining the magnetic developer. While the roller is shown as a plurality of pole pieces and magnetic washers, it is understood that any cylinder having magnetic lines of force emanating therefrom could readily be employed. Each of these rollers is mounted for rotation adjacent the photoconductive surface in the xerographic development zone by a rotatable shaft 29 mounted in the side support members 24. Each of the support shafts 28 has associated therewith a gear 30 which intermeshes to drive the various rollers in the direction as shown in FIG. 2. With this arrangement, each roller rotates in a direction opposite to the direction of rotation of each adjacent roller. A suitable source of power 31 may be employed to impart the motive forces to the gears 30, shafts 28, and cylinders 25 and 26.

The cylinders 25 and 26 are spaced a slight distance from each other and are provided, near their uppermost extents, with scraper blades 32 and 34 near or in contact therewith to remove the developer moved into contact therewith. Thus, when the lowermost magnetic roller attracts developer from the sump 22, it will rotate such magnetic developer in a brush-like orientation into contact with the latent electrostatic bearing surface being developed. Rotation of the cylinder to the uppermost position will permit the developer to be scraped from the lowermost cylinder by the scraper blade 32. The relatively loose developer will then be entrained by the next higher cylinder which will act as a non-developing transport cylinder to magnetically carry the developer to its uppermost position where it will again be scraped by a reverse oriented scraper blade 34. After being scraped, the developer is temporarily in a loose mass whereby its internal turbulence and internal agitation permits some of the more freshly toned developer, previously contacting the cylinder to reorient itself near the external tip of the brush. This ensures freshly toned developer to contact the image during each brushing of the image. Furthermore, the internal developer agitation increases the triboelectric characteristic of the developer. The developer at this time will be magnetically entrained by the third cylinder which, like the first one, functions as a magnetic brush developing cylinder. This procedure will then be continued up any number of magnetic cylinders until it is entrained by the uppermost magnetic cylinder. The uppermost magnetic cylinder has a final scraping plate 36 near or in contact therewith to permit the developer to be moved from the magnetic field due to the location and orientation of the last scraper plate 36 as assisted by gravity.

The use of five rollers in this assembly has been selected for illustrative purposes. Any number of rollers could readily be employed so long as alternate magnetic cylinders function for development purposes while intermediate cylinders function as transport members. Note is taken that the transport cylinders 25 are shown smaller and more remote from the photoconductor than developer cylinders 26. They could, however, be formed of the same size. The developer cylinders 26 must be loctaed adjacent the photoconductor to effect development.

Upon being scraped and gravity dropped by the uppermost cylinder and scraper blade 36, the developer gravity falls back toward the sump 22. Guide plate 38 is positioned to direct the developer to the sump while keeping it away from the rotating magnetic rolls 26 in the development zone.

Positioned on the side of the guide plate 38 over which the developer flows is a set of developer cross-mix baffles 40. These bafiles are arranged in a snow plow-type fashion to cause the developer cascading to the sump to be intermixed for permitting an even distribution of fully toned developer across the length of the development zone. Furthermore, the cross-mixing of developer increases the triboelectric relationship between toner and carrier. This feature of the instant invention eliminates the need for power driven cross mixing developer augers within the sump. Note is also taken that the alternate conveying and developing by the disclosed apparatus permits positioning of the development apparatus in a vertical or horizontal arrangement, at virtually any angle therebetween or even adjacent a curved sector of the photoconductor.

Shown in FIG. 3 is an alternate arrangement for the magnetic rollers 25 and 26 as shown in FIGS. 1 and 2. Except for the arrangement of these cylinders and the elimination of scraper blades 32 and 34, the device is the same as that shown in the embodiment of FIGS. 1 and 2. According to the FIG. 3 embodiment, the magnetic cylinders are each formed with non-magnetic rotatable hollow cylinders 44 and 46 arranged to rotate in alternating directions in the same manner as that shown in FIGS. 1 and 2. Each of these cylinders has an associated gear member or the like for imparting the alternating directions thereto. The cylinders 44 and 46 as well as gears employed for rotating the cylinders are connected to a suitable source of power, not shown, for imparting motion thereto.

Located within each of the cylinders is a magnet, preferably permanent, with north and south poles extending the length of the magnet cylinders with their field producing poles facing in the direction over which the developer will be moved. For example, within the lowermost, third and uppermost cylinders 44, the poles of the magnets face toward the photoconductor surface to be developed for the presentation of magnetic brush developing material to the image. The field producing magnets of the intermediate cylinders 46 which function to merely transport the developer have their field producing poles in a direction away from the photoconductive surface. Thus, when the cylinders are rotated, magnetic. developer will be entrained by the magnetic fields emanating through the lowermost rotating cylinder to cause developer to move in brushing contact with the photoconductive surface.

Upon reaching the uppermost position of lowermost cylinder 44, the magnetic developer is passed beyond the effect of the magnetic field of cylinder 44 into the effect of the magnetic field emanating from the next adjacent roller 46. In this manner, the developer may be magnetically attracted and then conveyed between adjacent cylinders from the uppermost position of a lower cylinder to the lowermost position of the next higher cylinder. This procedure continues until the developer contacts the uppermost roller whereafter, continued cylinder rotation will permit the developer to be dropped onto guide plate 36 inasmuch as it is no longer within the field of influence of any magnetic field producing means. The developer then gravity drops towards the sump over a suitable guide plate and cross-mix bafiies as described with respect to the embodiment of FIGS. 1 and 2. Note is taken that in this second embodiment the orientation of the magnet and cylinders permit the movement of developer from one roll to the other without the use of the scraper plates required in the embodiment of FIGS. 1 and 2.

While the instant invention as to its objects and advantages has been described herein as carried out in a specific embodiment thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the scope of the appended claims.

What is claimed is:

1. Apparatus for developing latent electrostatic images on a supporting member with magnetic developer includmg a plurality of cylinder means rotatable about parallel axes and having fields of magnetic force emanating therefrom, each of said cylinder means being closely spaced from each adjacent cylinder with at least some of said' cylinder means being spaced from the member for the development thereof by developer magnetically entrained by said cylinder means, said plurality of cylinder means also including other cylinder means intermediate the cylinder means which are adapted for development,

means to rotate each of said cylinder means in a direction of rotation opposite from the next adjacent cylinder means and sump means capable of retaining a quantity of developer adjacent an endmost cylinder means so that developer entrained thereby will be conveyed along the various cylinder means to a location remote from the endmost cylinder with alternate cylinder means functioning to develop the member with the magnetic developer material.

2. The apparatus as set forth in claim 1 wherein each of said cylinder means is provided with a scraper plate for the removal of developer therefrom.

3. The apparatus as set forth in claim 1 where each of said cylinder means is hollow and non-magnetic and is provided with fixed magnetic means interior thereof to entrain developer brought into contact with the surface of said cylinder means.

4. The apparatus as set forth in claim 1 wherein the axes of rotation of said cylinder means are disposed one above the other and further including developer directing plate means to guide developer from the uppermost cylinder towards the sump under the influence of gravity.

5. The apparatus as set forth in claim 4 and further including cross-mix bafiies on the developer directing plate means to cause the cross-mixing of developer cascaded thereacross on its pth of travel back to the sump.

References Cited UNITED STATES PATENTS 3,133,834 5/1964 Sowiak 118-6 37 3,306,193 2/1967 Rarey et a1. 118 637X FOREIGN PATENTS 17,228 1965 Japan 118-637 PETER FELDMAN, Primary Examiner US. Cl. X.R. 11717.5 

